This invention relates to seat cushions for use in seats of automobiles and various types of furniture, and more particularly to a seat cushion which is covered at its surface with a seat surface covering of fabric or like material of bag-like structure and which is packed thereinside with a mass of foamed synthetic resin material such as foamed polyurethane bonded to the seat surface covering.
A covering material such as a fabric material with or without a vinyl coating is most commonly used in many of prior art seat cushions for seats in automobiles. One of typical prior art processes employed for the manufacture of a seat cushion of this kind comprised the steps of cutting a web of fabric material with or without a vinyl coating into pieces correspondind to the portions including the seating portion and side portions, sewing together these pieces of fabric material to form a seat surface covering of bag-like structure, inserting a filler pad of cushion providing material such as foamed polyurethane into the internal space of the seat surface covering of bag-like structure, and mounting the resultant assembly on a seat frame provided with springs.
However, such a prior art manufacturing process required an extended time and a lot of labor. In addition, the prior art process was defective in that twists and creases impairing the beautiful appearance of the products occurred frequently, and some of the products were extremely distorted to such an extent that the remedy thereof required also an additional extended time and much labor together with an additional cost.
In an effort to obviate these prior art defects, there has been recently proposed a seat cushion manufactured by applying a back coating of vinyl or like material to a seat-covering providing fabric material, heating the fabric material, shaping the fabric material into the form of a seat surface covering of bag-like structure by use of shaping dies or any other suitable means, and in lieu of inserting a filler pad of cushion providing material into the seat surface covering of bag-like structure, injecting a solution of polyurethane into the internal space of, the seat surface covering of bag-like structure to integrally mold foamed polyurethane with the seat surface covering being retained between the dies. Such an integral molding process obviates the aforementioned prior art defects, and distinct embossed pattern can be produced on the product.
However, such a method finds a limited application and is only applicable to vinyl-coated fabric materials or fabric materials having a back coating of vinyl chloride or like material. Further, in the product obtained by the integral molding of foamed polyurethane with the seat surface covering of fabric material, the polyurethane solution tends to penetrate through the texture thereby hardening the seat surface covering or producing blurs on the surface thereof, or the solution may solidify to impair the otherwise beautiful appearance of the product. Thus, the seat cushion obtained by the proposed method has been defective in that its seat surface covering has no permeability to air, the otherwise beautiful external appearance is impaired, and the seat cushion does not provide the desired comfortableness to sit thereupon.
A pair art seat cushion obtained by bonding a filler pad of foamed polyurethane to a seat surface covering of fabric material of bag-like structure has also been defective in that a thin layer tending to be formed on the surface of the filler pad of foamed polyurethane by, for example, the mold releasing agent used in the molding step deteriorates the permeability to air and acts as a source of unusual noise, and also, separation of the bonded portions together with stripping of the thin surface layer tends to occur.
Further, in the seat cushion manufactured by the prior art process of integral vacuum molding of a foamed synthetic resin material such as foamed polyurethane with a vinyl-coated or vinyl-backed fabric material which provides the seat surface covering, a fault during the formation of the seat surface covering or during the molding of the foamed polyurethane gives rise to necessarily a counter-fault in the other. For examplem a large void produced within the molded layer of foamed polyurethane or similar void produced at the interface between the seat surface covering and the molded layer of foamed polyurethane is very difficult to remedy, and this difficulty has been the greatest problem encountered with the seat cushions manufactured by the integral vacuum molding process.
The material cost of the seat surface covering of the seat custion has become considerably high when a single piece of highly extensible fabric material is used to continuously cover the seat cushion portions including the seating portion and side portions to meet a specification requirement. Further, when the seat custion includes undercuts in its side portions, shaping dies of inversely tapered configuration have been required resulting in difficulty of shaping the seat surface covering into the desired form.